| French Republican Calendar | France (Revolutionary period) | Adopted 1793 CE Wikipedia+1 | 12 months × 30 days + 5 complementary days (6 in leap years); months divided into three 10-day “décades” (weeks of 10 days) Wikipedia+1 | Leap year when needed to align with the tropical year (complementary leap day) webexhibits.org+1 | Motivated by Enlightenment ideals; replaced Gregorian for a time. Few nations adopted; discontinued by Napoleon in 1806. Still studied for reform proposals. |
| Bahá’í (Badíʿ) Calendar | Global Bahá’í Faith | Established mid-19th century (1844 CE; confirmed 1870s) Wikipedia | 19 months × 19 days = 361 days + 4-5 intercalary days (Ayyám-i-Há) to align with vernal equinox; each month named after an attribute of God Wikipedia+1 | Intercalary days inserted before final month so that year ends on day before next equinox; the equinox in the Northern Hemisphere sets New Year (Naw-Rúz) Wikipedia+1 | Used by Bahá’ís for religious observances worldwide; shows how arithmetic calendars can incorporate symbolism. Does not intend to replace civil calendars in most countries. |
| International Fixed Calendar (Cotsworth calendar) | Proposed / reformist (UK / international advocates) | Early 20th century proposals; used by Kodak internally mid-20th century | 13 months of 28 days each (each month = 4 weeks); one “Year Day” outside any week; leap years add one extra day similarly | Leap rule often tied to Gregorian leap years; extra day in leap years; but “Year Day” (or “New Year’s Day”) not part of any week | Never adopted at national level; periodic interest in business / productivity circles. Illustrates perennial / symmetry motivations in calendar reform. |